Fatty acid digestion, synthesis and metabolism in broiler chickens and pigs

<br /> The impact of variation in the composition of dietary fat on digestion, metabolism and synthesis of fatty acids was studied in broiler chickens and in pigs. In young broiler chickens, digestion of unsaturated fatty acids was substantially higher compared with that of saturated fatty acids. Positional distribution appeared important. Particularly digestion of saturated fatty acids, e.g. palmitic acid (C16:0), esterified at the sn-1 and -3 position of the glycerol backbone was lower (51%) compared with that observed at the sn-2 position (90%). Based on these observations, an equation was developed predicting the digestion of dietary fat sources in broiler chickens and pigs, taking fatty acid composition, the positioning, and the proportion of free fatty acids into account. The deposition of fat, especially of monounsaturated fatty acids in body tissues, increased in broilers by feeding saturated fats in comparison with unsaturated fats caused by both a reduced &szlig;-oxidation and an increased rate of de novo synthesis of fatty acids. In a feeding trial with pigs, starch, saturated and unsaturated fatty acid sources were compared at similar intakes of net energy. Growth performance and backfat thickness were unaffected by dietary energy source. Intramuscular fat content, however, tended to be increased in starch fed pigs when compared with pigs fed the saturated fatty acid source. To study the interactions between dietary linoleic acid (LA; C18:2 n-6) and -linolenic acid (ALA; C18:3 n-3) and their impact on the synthesis of long-chain polyunsaturated fatty acids (LC-PUFA) in both the n-3 and n-6 chains, a trial was designed in which identical increments in the intake of ALA and LA were fed to growing pigs. Generally, dietary LA inhibited the synthesis of n-3 LC-PUFA in the liver. Dietary ALA increased the content of eicosapentaenoic acid (EPA; C20:5 n-3) but decreased that of docosahexaenoic acid (DHA; C22:6 n-3) in the liver. DHA levels in brain were hardly affected by both dietary LA and ALA. It was concluded that in addition to &Delta;6 desaturase, elongase 2 might be a rate-limiting enzyme in the formation of DHA. The impact of these findings on the potential of contribution of feeding LA and ALA to pigs to meet human dietary requirements for LC-PUFA by meat products was investigated by analysing the fatty acid composition of muscle and fat tissues. It appeared impossible to attain substantial improvements in tissue DHA contents by feeding different combinations of LA and ALA. However, EPA of intramuscular fat can be increased by feeding ALA, particularly when restricting LA intake. In addition, docosapentaenoic acid (DPA; C22:5 n-3) was increased in both muscle and backfat by dietary ALA. DPA might have comparable biological effects as EPA. The potential of meat products to supply DPA in food is considerable and therefore of interest. &nbsp; &nbsp